Short-lived radionuclides that emit alpha particles are particularly insidious radiological poisons for humans and animals. The large mass and electric charge of alpha particles precludes their transmission beyond a few millimeters. However, in the case of a short-lived radionuclide the short half-life means that the radionuclide is emitting large numbers of energetic particles that, on a per molecule basis, deliver about 6 orders of magnitude as much energy as a chemical explosive. If the alpha-particle emitting radionuclide is within a human body this energy is very efficiently delivered to the body's nearby cells. Consequently, very large radiological doses can be delivered by small amounts of material, generally resulting in illness or death. The alpha particles themselves typically cannot be directly detected because substantially all of the alpha particles are absorbed by the body. Some alpha-particle emitters also emit gamma rays that can be detected, but some alpha-particle emitting radionuclides may emit little or no associated gamma radiation. If the daughter products of these radionuclides are stable or also emit little or no associated gamma rays, this radiological poison may be very difficult to detect within the body or within container that has even very simple shielding.
These properties make such radionuclides candidates for covert poisons or terror weapons. For instance, 210Po is easily made by persons with access to nuclear reactors. 210Po emits essentially no gamma or beta radiation and its daughter (206Pb) is stable. If properly distributed, a few 10's of grams of 210Po could contaminate the air in a large room or chamber (up to even a half million cubic feet) with about one-tenth of a lethal dose per liter. An individual dose of about 1 microgram would be almost certainly lethal to the recipient.
It would be very useful to have improved means of detecting 210Po and similar alpha-particle emitting nuclei. Such means would likely also have utility for detection of other alpha-particle emitting nuclei that also emit gamma radiation.